Method for switching operating carrier at a user equipment in wireless communication system

ABSTRACT

A device and method of operating carriers at a user equipment in a wireless communication system includes: configuring, by the user equipment, a plurality of carriers including a first carrier and a second carrier; receiving control information on an activation of the second carrier among the plurality of carriers; activating the second carrier; and deactivating the activated second carrier after a certain amount of time. The certain amount of time is based on a valid time of the activation of the second carrier. The valid time is defined by a number of frames.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/021,912, filed on Sep. 9, 2013, now U.S. Pat. No. 9,137,791, which isa continuation of U.S. application Ser. No. 13/124,117, filed Apr. 13,2011, now U.S. Pat. No. 8,554,225, which is the National Stage filingunder 35 U.S.C. 371 of International Application No. PCT/KR2010/001576,filed on Mar. 12, 2010, which claims the benefit of U.S. ProvisionalApplication No. 61/159,447, filed on Mar. 12, 2009, the contents of allof which are incorporated by reference herein in their entireties.

TECHNICAL FIELD

The present invention relates to wireless communication, more specially,the present invention relates to a method for switching operatingcarrier at a user equipment (UE).

BACKGROUND ART

In a system where multiple carriers may be used for UE operationssimultaneously, the carrier assignment to each UE is important issuesince the way to manage system carriers should be optimized to achievemaximal system performance and throughput. The situation may happen atthe time of UE initial access to system, UE handover, carrier loadbalancing, multi-cell operation on specific carrier(s), per-UE trafficvariation, and so on. During these cases, an eNB may need to reorganizethe carrier utilization scheme of each UE so that specific carrier maybe empty or managed to the target status, while UE have to retain thesustained service provision from the corresponding eNB(s). Multiple eNBsor cells may be responsible to this change (e.g., situation of CoMPoperation).

However, in a system where multiple carriers may be used for UEoperations simultaneously, a method of managing the carrier assignmenthas not studied yet.

DISCLOSURE OF INVENTION Technical Problem

Accordingly, the present invention is directed to a method for switchingoperating carrier in a wireless communication system that substantiallyobviates one or more problems due to limitations and disadvantages ofthe related art.

Solution to Problem

To achieve these objects and other advantages and in accordance with thepurpose of the invention, as embodied and broadly described herein, Amethod for switching operating carrier at a user equipment (UE) inwireless communication system includes receiving target carrierinformation indicating a target carrier of the UE and target carriertransition time information indicating a time difference betweenreceiving timing of transition indication and transition completiontiming from an base station (BS); and switching a current operatingcarrier to the indicated target carrier based on the received the targetcarrier transition time information and the target carrier information.

Preferably, the method further include transmitting a ACK/NACK confirmsignal indicating whether the target carrier transition time informationand the target carrier information is received without error via on thetarget carrier to the base station.

Alternatively, the method further include transmitting a ACK/NACKconfirm signal indicating whether the target carrier transition timeinformation and the target carrier information is received without errorvia on the target carrier and the current operating carrier to the basestation.

In another aspect of the present invention, a user equipment (UE) forswitching operating carrier in wireless communication system includes areceiving module for receiving target carrier information indicating atarget carrier of the UE and target carrier transition time informationindicating a time difference between receiving timing of transitionindication and transition completion timing from an base station (BS);and a switching module for switching from a current operating carrier tothe indicated target carrier based on the received the target carriertransition time information and the target carrier information.

Preferably, the UE further include a transmitting module fortransmitting a ACK/NACK confirm signal indicating whether the targetcarrier transition time information and the target carrier informationis received without error via on the target carrier to the base station.

Alternatively, the UE further include a transmitting module fortransmitting a ACK/NACK confirm signal indicating whether the targetcarrier transition time information and the target carrier informationis received without error via on the target carrier and the currentoperating carrier to the base station.

Advantageous Effects of Invention

According to a method for switching operating carrier at a userequipment of the present invention, one or more component carriers maybe assigned to a UE as special carriers. This management proceduresrelated with the special carriers may be utilized as load balancing orother system management or system-wise/cell-group wise coordinationpurposes.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention. In the drawings:

FIG. 1 illustrates a radio frame structure of 3GPP LTE;

FIG. 2 illustrates disjoint carrier usage model according to embodimentsof the present invention;

FIG. 3 illustrates overlapped carrier usage model according toembodiments of the present invention;

FIG. 4 illustrates a case that multiple cell-specific anchor carriers isallocated for a UE according to embodiments of the present invention;and

FIG. 5 is a diagram for configuration of a user equipment apparatusaccording to one preferred embodiment of the present invention.

FIG. 6 illustrates a method of operating carriers by a user equipment(UE) in a wireless communication system including a plurality ofcarriers including a primary and at least one additional carrier.

FIG. 7 illustrates a user equipment (UE) of operating carriers in awireless communication system including a plurality of carriersincluding a primary carrier and at least one additional carrier.

FIG. 8 illustrates a method of operating carriers by a network in awireless communication system including a plurality of carriersincluding a primary and at least one additional carrier.

FIG. 9 illustrates a network of operating carriers in a wirelesscommunication system including a plurality of carriers including aprimary carrier and at least one additional carrier.

BEST MODE FOR CARRYING OUT THE INVENTION

Reference will now be made in detail to the exemplary embodiments of thepresent invention with reference to the accompanying drawings. Thedetailed description, which will be given below with reference to theaccompanying drawings, is intended to explain exemplary embodiments ofthe present invention, rather than to show the only embodiments that canbe implemented according to the invention. The following detaileddescription includes specific details in order to provide a thoroughunderstanding of the present invention. However, it will be apparent tothose skilled in the art that the present invention may be practicedwithout such specific details. For example, the following detaileddescription is given under the assumption that a mobile communicationsystem is a 3GPP LTE system. However, the description is applicable toany other mobile communication systems except for specific features ofthe 3GPP LTE system.

In some instances, known structures and devices are omitted, or areshown in block diagram form focusing on important features of thestructures and devices, so as not to obscure the concept of the presentinvention. The same reference numbers will be used throughout thisspecification to refer to the same or like parts.

In the following description, ‘mobile station (MS)’ is assumed to referto a mobile or fixed user end device such as a user equipment (UE), and‘base station (BS)’ is assumed to refer to any node of a network end,such as a node B and an eNode B, communicating with the MS. Also,femtocell BS may be referred to femtocell access point (FAP).

In a mobile communication system, an MS may receive information from aBS through a downlink and the MS may transmit information to the BSthrough an uplink. Information transmitted or received by the MSincludes data and control information. There are various physicalchannels according to types and purposes of information transmitted orreceived by the MS.

Techniques, apparatus and systems described herein can be used invarious wireless access technologies such as code division multipleaccess (CDMA), frequency division multiple access (FDMA), time divisionmultiple access (TDMA), orthogonal frequency division multiple access(OFDMA), single carrier frequency division multiple access (SC-FDMA),etc. The CDMA may be implemented with a radio technology such asUniversal Terrestrial Radio Access (UTRA) or CDMA2000. The TDMA may beimplemented with a radio technology such as Global System for Mobilecommunications (GSM)/General Packet Radio Service (GPRS)/Enhanced DataRates for GSM Evolution (EDGE). The OFDMA may be implemented with aradio technology such as institute of electrical and electronicsengineers (IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20,evolved-UTRA (E-UTRA) etc. The UTRA is a part of a universal mobiletelecommunication system (UMTS), 3rd generation partnership project(3GPP) long tem evolution (LTE) is a part of an evolved-UMTS (E-UMTS)using the E-UTRA. The 3GPP LTE employs the OFDMA in downlink and employsthe SC-FDMA in uplink. LTE-advance (LTE-A) is an evolution of the 3GPPLTE. For clarity, this application focuses on the 3GPP UTE/LTE-A,However, technical features of the present invention are not limitedthereto.

FIG. 1 illustrates a radio frame structure of 3GPP LTE.

Referring to FIG. 1, a radio frame may include 10 subframes. A subframemay include two slots in time domain. A time for transmitting onesubframe is defined as a transmission time interval (TTI). For example,one subframe may have a length of 1 millisecond (ms), and one slot mayhave a length of 0.5 ms. One slot includes a plurality of orthogonalfrequency division multiplexing (OFDM) symbols in time domain. One slotmay include 7 symbols. Since the 3GPP LTE uses the OFDMA in thedownlink, the OFDM symbol is for representing one symbol period. TheOFDM symbol may also be referred to as an SC-FDMA symbol or a symbolperiod. A resource block (RB) is a resource allocation unit, andincludes a plurality of contiguous subcarriers in one slot. Thestructure of the radio frame is shown for exemplary purposes only. Thus,the number of subframes included in the radio frame or the number ofslots included in the subframe or the number of OFDM symbols included inthe slot may be modified in various manners.

Carrier assignment may be categorized into several aspects as follows.

1) Single carrier may be allocated to a user equipment (UE) as anchorcarrier. 2) Multiple carriers may be allocated a UE for active carrier.3) Carrier index to be used by a UE may be changed. 4) Specific carrieramong UE-specific assignment carrier may be removed. 5) Which carrieramong UE operation carrier set is anchor carrier is notified to a UE.

These carrier assignment methods need to be considered and carefullydesigned so that UE QoS is not degraded. In the following, correspondingprocedure/methods will be disclosed.

Carrier management may be performed in various types. More specifically,carrier management may be performed in a manner of single carrier usagemodel or multiple-carrier usage model according to the managementtarget.

First, single carrier management method will be described.

Single carrier management may be defined as assignment of single carrierto a UE, de-assignment of single carrier from the UE, carrier identity(e.g., carrier index) switching from one property to another property.In this case, the property may be carrier index, carrier usage model,power control model, etc.

For example, we may consider a case where a UE uses single carrier andanother carrier instead of currently being-used carrier may be used forthe UE. This situation occurs when the UE performs initial access to acell or the UE performs handover. Since the UE does not know the systemstatus or scheduler status during the initial access, it can result inan un-balanced carrier usage or it can cause an eNB to waste frequencyresource due to unnecessary duplicated control information transmission.With this drawback or defect, the eNB would try to move the currentlyoperating carrier of the UE to another carrier which would not causesuch problems. Procedure for switching this operating carrier may bedefined as following.

FIG. 2 illustrates disjoint carrier usage model according to embodimentsof the present invention.

An eNB may determine if the carrier used by a UE does cause any drawbackto system or UE operation S210. If it does, the eNB performs next step.Otherwise, the eNB may repeat the step of S210. The eNB may thenindicate the target carrier to the UE S220. The UE may switch from thecurrent operating carrier to the designated target carrier S230. Afterswitching from one carrier to another one is finished, the eNB performsthe step of S210. It is noted that the way to allocate the targetcarrier and the UE behavior may be differently defined depending on thetarget QoS management. For example following schemes can be envisioned.

As shown in FIG. 2, in disjoint carrier usage model, there is nooverlapped region on each carrier usage interval 210 and 220. That is,the region of previously used carrier 210 is perfectly not overlappedwith region of new carrier 220 in time domain. In this case, the targetcarrier movement indication of the eNB may include following features.

As shown in FIG. 2, target carrier transition time (Tt) 230 may mean atime difference between transition indication timing 240 and transitioncompletion timing 250. Here, the target carrier transition time (Tt) 230may be called as valid time, transition gap, etc. The target carriertransition time (Tt) 230 may be measured from receiving timing oftransition indication 240 and transition completion timing 250 at theUE. If the UE receive target carrier information indicating targetcarrier and target carrier transition time information including timerequired for transiting to target carrier from the eNB, the UE may movefrom current carrier 210 to the indicated target carrier 220 based onreceived the target carrier transition time information and targetcarrier information.

The target carrier transition time (Tt) 230 is defined such as OFDMsymbol positions/intervals/numbers, subframepositions/intervals/numbers, or radio frame positions/intervals/numbers.In case of single carrier transition, the position or intervalinformation may be entity. If multiple carrier transitions are defined,the positions or interval information may be multiple entity whichrepresenting the target carrier transition time from one carrier to theother carrier.

After the UE complete to transit to the target carrier 220, the UE mayexplicitly or implicitly transmit ACK/NACK confirmation signalingindicating whether carrier switching of the UE is successful to the eNB.This ACK/NACK confirmation information may not be necessary if controlmessage including the target carrier information and the target carriertransition time 230 is transmitted by high layer signaling, that is, nota L1/L2 signaling without ACK/NACK response.

However, if this ACK/NACK confirmation information is transmitted byL1/L2 control signaling, then the ACK/NACK indication is transmitted tothe eNB. The ACK/NACK indication bit may play a role of protocolrobustness. If there is no ACK/NACK confirmation on the transition totarget carrier 220, then the eNB needs to fall back to old UE carrierconfiguration. In this case, error may be occurred.

Target carrier information indicating target carrier 220 may berepresented as type of target carrier index. This target carrier indexmay be bitmap information having a predefined sizes, the predefined sizemay be represented as the total usable system carrier in thecorresponding eNB. The target carrier index may be a simple index valuecounted according to frequency axis.

If the eNB wants to confirm the transition or measure the target carrier220, the eNB may indicate information including behavior of the UE onthe target carrier 220 to the UE.

In case of traffic transaction during the carrier transition of a UE,the ACK/NACK information on the UL PUSCH (Physical Uplink SharedCHannel)/(DL PDSCH) transmission need to be received from the targetcarrier 220. More specially, the UE may transmit the ACK/NACK confirminformation to the eNB via the target carrier 220.

FIG. 3 illustrates overlapped carrier usage model according toembodiments of the present invention.

If capability of a UE is allowed, the UE, may use the old carrier 310and new carrier 320 simultaneously. In this case, the requiredinformation may be the same with disjoint carrier usage model in FIG. 2.However, since the ultimate used carrier is one, it is necessary todefine what happens at during overlapped interval of carrier usage 340.Termination of old carrier 310 usage may be initiated by decision of aneNB or indication of the UE. Decision of the eNB or indication of the UEfor usage termination of old carrier 310 will be further describedbelow.

If a UE use temporally multiple carrier, then the transmission of datatraffic or ACK/NACK confirm may be duplicated when there is ambiguity ofwhich carrier is used by the UE. For example, the target carrier isdownlink carrier, the old carrier (or previously used carrier) 310 andtarget carrier 320 may include same control information such asscheduling grant and the same data traffic. To determine whether the UEcompleted the transition to target carrier 320, the eNB need todiscriminate which carrier is being used. To enable this functionality,the eNB may allocate slightly different grant information or ACK/NACKresource. For example, uplink ACK/NACK transmission may be controlled byCCE (Control Channel Element) index or DM RS (DeModulation ReferenceSignal) indication or different PUSCH allocation. On the other hand,this may be determined with carrier usage timer on the old carrier 310in similar to disjoint carrier usage model.

In case that termination of old carrier 310 usage is determined byindication of the UE, the UE may transmit special information via theold carrier 310 or target carrier 320 or about the transition itself.For example, if UL carrier is changed from one carrier to anothercarrier, the UE may transmit special information (e.g., transmittingscheduling request or sounding transmission on the target carrier). IfDL carrier is changed from one carrier to another carrier, the UE maytrigger a scheduling request and transmit control information on thecarrier transition completion.

It is noted that this single carrier may be an anchor carrier or normalcarrier. The anchor carrier may be used for transmitting main controlinformation such as system information, physical control channel,UE-specific or UE group-specific control in formation, etc. And thenormal (active) carrier is for data transaction or measurement orlimited control information.

The method of adding one carrier to a UE operating carrier set orremoving one carrier from the UE operating carrier set may be alsoimplemented by following procedure.

An eNB may indicate one carrier which to be added to the UE or removedfrom the UE. This control signal indicating carrier to be added to theUE or removed from the UE may be defined as RRC (Radio Resource Control)signal or L1/L2 control signaling. Preferably, the control signalincludes the target carrier information, which may be represented bybitmap or logical index or physical carrier value. In addition, thecontrol signal further includes the corresponding valid time or starttime for the removed carrier or new carrier.

A UE needs to respond with ACK/NACK confirmation on the control signal.In this case, the carrier addition or removal is needed to check in boththe UE and the eNB sides so that any protocol breach does not happen.This double check may be realized with simply high layer signaling orACK/NACK response in both DL and UL directions.

For example, a UE may receive a control command from an eNB. However,the UE may not know whether the eNB received response of the UE.Therefore, additional ACK/NACK regarding the response of the UE isneeded to transmit to the UE. This double check may be also applicableto previous carrier switching case as described in FIG. 2.

After predefined time duration, a removed carrier is invalidated and notbe used as normal carrier or anchor carrier. In case of carrier removal,the time duration may be presumed to be zero. In contrary, if a carrieris to be added to a UE operating carrier set, it is validated at theindicated start time or after indicated time duration.

As described above, single carrier management method is described.Hereinafter, multiple carrier management methods will be described.

Even though multiple carriers are allocated or switched or removed, thebasic principle does not change significantly compared to the singlecarrier management case. Since multiple carriers are involved in thecarrier allocation procedure, it is needed to consider the case that allthe carriers should be simultaneously changed or not. If all theinvolved carriers are changed simultaneously, then every proceduredefined in single carrier management method may be reused except formultiple carrier lists. Here, the multiple carrier lists may be alsorepresented as bitmap or carrier indices.

However, if anchor carrier(s) among the multiple carriers exists,overall operation may be defined via the anchor carrier. That is,carrier management request may be delivered through an anchor carrierand corresponding change result or request processing result may be alsodelivered via designated anchor carrier if uplink anchor carrier exists.

Hereinafter, the method of indicating which carrier is an anchor carrierindication will be described.

If a UE is utilizing multiple carriers, overhead due to using themultiple carriers may be occurred, and redundant information may betransmitted. For example, if the UE receives system information, thenthe corresponding system information is needed to transmit on everydownlink carrier. Transmission of the corresponding system informationwill waste frequency resource without any help to the UE operation.However, since the UE does not know which carrier will transmit theexpecting control information, the UE may need to decode blindly everydownlink carrier in order to detect a specific control channel.Therefore, to reduce the decoding complexity and frequency resourcewaste, to enhance performance of the multi-carrier operation as much aspossible, one or more special carriers are preferably included inmultiple carriers so that those carriers are responsible for the commonsystem information or UE-group or UE-specific control information. Thiscarrier may be called as anchor carrier, primary carrier, or referencecarrier, etc. One or more specific carriers among the multiple carrierused by a UE is defined as cell-specific anchor carriers or UE-specificanchor carriers.

FIG. 4 illustrates a case that multiple cell-specific anchor carriersare allocated for a UE according to embodiments of the presentinvention.

One or more specific carriers may be defined as cell-specific anchorcarriers or UE-specific anchor carriers depending on the systemconfiguration. If cell-specific anchor carriers are defined, then it isobvious that the UE can receive the required control information onlywhen decoding those cell-specific anchor carriers. However, even thoughcell-specific carrier may be defined, if a UE utilizes multiplecell-specific anchor carriers 410 and 420 as its own component carriers,then UE is still necessary to decode multiple downlink carriers toreceive system information. Therefore, it is more efficient to selectminimum number of anchor carriers which are the target carrier(s) to bemonitored by the UE.

The method of indicating which carrier is anchor carrier among multipleUE carrier set may be one or combination of following methods.

For instance, cell-specific anchor carrier becomes UE-specific anchorcarrier when it has the lowest/highest carrier index/value and belongsto UE carrier set. In this case, an eNB may directly notify UE-specificanchor carrier to the UE.

An eNB may directly indicate anchor carrier to a UE using bitmap orcarrier index when single or multiple carriers are assigned to the UE.It is noted that if whole carriers used by a OF are not defined in aspecific time, then the anchor carrier definition may be duplicated. Inthat case, the latest anchor carrier indication can override theprevious setting or multiple anchor carriers may be allowed.

Anchor carrier may be changed from one carrier to the other carrierdepending on system load/operating environment. In this case, new anchorcarrier index may be explicitly informed to the UE or may be nextlowest/highest carrier index/value.

It is noted that anchor carrier may be set at the end of random accessprocedure through high layer signaling or L1/L2 control signaling. If aUE wants to change anchor carrier, then random access procedure may beinitiated.

Periodic high layer signaling indicating which anchor carrier is theUE's anchor carrier may be transmitted to the UE. In this case, theperiodic high layer signaling may include all the anchor information ofmultiple UEs, the signaling is broadcasted to UEs.

Multiple anchor carriers may be defined and modified depending on the UEoperation mode such as MIMO, Coordinated Multi-Point (CoMP), or LTE-Afeatures. Anchor carrier may behave differently depending on the UEtransmission mode or operation mode on that carrier or anchor-specificsupplementary carriers.

Anchor carrier control message may be defined with high layer signaling(e.g., RRC) or L1/L2 control signaling, where anchor carrier specificmessage may be defined separately from carrier allocation message, orjointly defined so that carrier set indication and anchor carrierindication may always be informed simultaneously.

FIG. 6 illustrates a method of operating carriers by a user equipment(UE) in a wireless communication system including a plurality ofcarriers including a primary and at least one additional carrier.

Referring to FIG. 6, the UE receives from a network, a first signalingindicating which carrier among the plurality of carriers is configuredas the primary carrier. A carrier having a lowest carrier index amongthe plurality of carriers is configured as the primary carrier. The UEactivates an additional carrier of the plurality of carriers. The UEreceives, from the network, a second signaling instructing removing theadditional carrier. The UE removes the additional carrier based upon thesecond signaling. The UE configures another carrier of the plurality ofcarriers to a new primary carrier during a random access procedure.

FIG. 7 illustrates a user equipment (UE) of operating carriers in awireless communication system including a plurality of carriersincluding a primary carrier and at least one additional carrier.

Referring to FIG. 7, receiver of UE is configured to receive from anetwork, a first signaling indicating which carrier among the pluralityof carriers is configured as the primary carrier. A carrier having alowest carrier index among the plurality of carriers is configured asthe primary carrier. Processor of the UE is configured to activate anadditional carrier of the plurality of carriers. The receiver of the UEis configured to receive, from the network, a second signalinginstructing removing the additional carrier. The processor of the UE isconfigured to remove the additional carrier based upon the secondsignaling. The processor of the UE is configured to configure anothercarrier of the plurality of carriers to a new primary carrier during arandom access procedure.

FIG. 8 illustrates a method of operating carriers by a network in awireless communication system including a plurality of carriersincluding a primary and at least one additional carrier.

Referring to FIG. 8, the network transmits to a user equipment (UE), afirst signaling indicating which carrier among the plurality of carriersis configured as the primary carrier. A carrier having a lowest carrierindex among the plurality of carriers is configured as the primarycarrier. The network activates an additional carrier of the plurality ofcarriers. The network transmits, to the UE, a second signalinginstructing removing the additional carrier. The network removes theadditional carrier based upon the second signaling. The networkconfigures another carrier of the plurality of carriers to a new primarycarrier during a random access procedure.

FIG. 9 illustrates a network of operating carriers in a wirelesscommunication system including a plurality of carriers including aprimary carrier and at least one additional carrier.

Referring to FIG. 7, transmitter of the network is configured totransmit to a user equipment (UE), a first signaling indicating whichcarrier among the plurality of carriers is configured as the primarycarrier. A carrier having a lowest carrier index among the plurality ofcarriers is configured as the primary carrier. The processor of networkis configured to activate an additional carrier of the plurality ofcarriers. The transmitter of the network is configured to transmit, tothe UE, a second signaling instructing removing the additional carrier.The processor of the network is configured to remove the additionalcarrier based upon the second signaling. The processor of the network isconfigured to configure another carrier of the plurality of carriers toa new primary carrier during a random access procedure.

FIG. 5 is a diagram for configuration of a user equipment apparatusaccording to one preferred embodiment of the present invention

Referring to FIG. 5, the FE may include a receiving module 510,processor 520, a transmitting module 530, and memory 540.

The receiving module 510 may receive target carrier informationindicating a target carrier of the UE and target carrier transition timeinformation indicating a time difference between receiving timing oftransition indication and transition completion timing from an basestation.

Processor 520 may include a switching module 521. The switching module521 may switch a current operating carrier to the indicated targetcarrier based on the received the target carrier transition timeinformation and the target carrier information.

The transmitting module 530 may transmit a ACK/NACK confirm, signalindicating whether the target carrier transition time information andthe target carrier information is received without error via on thetarget carrier to the base station. Alternatively, the transmittingmodule 530 may transmit a ACK/NACK confirm signal indicating whether thetarget carrier transition time information and the target carrierinformation is received without error via on the target carrier andcurrent operating carrier to the base station.

Memory 540 may information calculated in the processor 520 for apredetermined period of time, and may be replaced with a buffer (notshown) or the like.

The embodiments described below are provided by combining components andfeatures of the present invention in specific forms. The components orfeatures of the present invention can be considered optional if notexplicitly stated otherwise. The components or features may beimplemented without being combined with other components or features.The embodiments of the present invention may also be provided bycombining some of the components and/or features. The order ofoperations in the embodiments of the present invention may be changed.Some components or features of one embodiment may be included in anotherembodiment or may be replaced with corresponding components or featuresof another embodiment.

The embodiments of the present invention may be implemented by variousmeans, for example, hardware, firmware, software, or a combinationthereof.

In a hardware configuration, methods according to the embodiments of thepresent invention may be implemented by one or more application specificintegrated circuits (ASICs), digital signal processors (DSPs), digitalsignal processing devices (DSPDs), programmable logic devices (PLDs),field programmable gate arrays (FPGAs), processors, controllers,microcontrollers, microprocessors, etc.

In a firmware or software configuration, methods according to theembodiments of the present invention may be implemented in the form ofmodules, procedures, functions, etc. which perform the above-describedfunctions or operations. Software code may be stored in a memory unit soas to be driven by a processor. The memory unit is located at theinterior or exterior of the processor and may transmit data to andreceive data from the processor via various known means.

The detailed description of the exemplary embodiments of the presentinvention has been given to enable those skilled in the art to implementand practice the invention. Although the invention has been describedwith reference to the exemplary embodiments, those skilled in the artwill appreciate that various modifications and variations can be made inthe present invention without departing from the spirit or scope of theinvention described in the appended claims. For example, those skilledin the art may use each construction described in the above embodimentsin combination with each other.

Accordingly, the invention should not be limited to the specificembodiments described herein, but should be accorded the broadest scopeconsistent with the principles and novel features disclosed herein.

INDUSTRIAL APPLICABILITY

The method for switching operating carrier at a user equipment (UE) in awireless communication system is applicable to IEEE 802.16m system, 3GPPLTE system, and like that.

What is claimed is:
 1. A method of operating carriers at a userequipment (UE) in a wireless communication system including a pluralityof carriers including a primary and at least one additional carrier, themethod comprising: receiving, by the UE from a network, a firstsignaling indicating which carrier among the plurality of carriers isconfigured as the primary carrier, wherein a carrier having a lowestcarrier index among the plurality of carriers is configured as theprimary carrier; activating, by the UE, an additional carrier of theplurality of carriers; receiving, by the UE from the network, a secondsignaling instructing removing the additional carrier; and removing, bythe UE, the additional carrier based upon the second signaling.
 2. Themethod of claim 1, wherein the primary carrier is UE-specificallyconfigured.
 3. The method of claim 1, wherein the first signalingincludes a radio resource control (RRC) signaling.
 4. The method ofclaim 1, wherein the second signaling includes a radio resource control(RRC) signaling.
 5. The method of claim 1, wherein the additionalcarrier is invalidated upon the removing.
 6. The method of claim 1,wherein the second signaling includes a carrier index of the additionalcarrier to be removed.
 7. The method of claim 1, further comprising:configuring another carrier of the plurality of carriers to a newprimary carrier during a random access procedure.
 8. A user equipment(UE) of operating carriers in a wireless communication system includinga plurality of carriers including a primary carrier and at least oneadditional carrier, the UE comprising: a receiver configured to receive,from a network, a first signaling indicating which carrier among theplurality of carriers is configured as the primary carrier, wherein acarrier having a lowest carrier index among the plurality of carriers isconfigured as the primary carrier, and a processor configured toactivate the additional carrier, wherein the receiver is furtherconfigured to receive, from the network, a second signaling instructingremoving the additional carrier, and wherein the processor is furtherconfigured to remove the additional carrier based upon the secondsignaling.
 9. The UE of claim 8, wherein the primary carrier isUE-specifically configured.
 10. The UE of claim 8, wherein the firstsignaling includes a radio resource control (RRC) signaling.
 11. The UEof claim 8, wherein the second signaling includes a radio resourcecontrol (RRC) signaling.
 12. The UE of claim 8, wherein the additionalcarrier is invalidated upon the removing.
 13. The UE of claim 8, whereinthe second signaling includes a carrier index of the additional carrierto be removed.
 14. The UE of claim 8, wherein the processor is furtherconfigured to configure another carrier of the plurality of carriers toa new primary carrier during a random access procedure.
 15. A method ofoperating carriers at a network in a wireless communication systemincluding a plurality of carriers including a primary and at least oneadditional carrier, the method comprising: transmitting, from thenetwork to a user equipment (UE), a first signaling indicating whichcarrier among the plurality of carriers is configured as the primarycarrier, wherein a carrier having a lowest carrier index among theplurality of carriers is configured as the primary carrier; activating,by the network, an additional carrier of the plurality of carriers;transmitting, from the network to the UE, a second signaling instructingremoving the additional carrier; and removing, by the network, theadditional carrier based upon the second signaling.
 16. The method ofclaim 15, further comprising: configuring another carrier of theplurality of carriers to a new primary carrier during a random accessprocedure.
 17. A network of operating carriers in a wirelesscommunication system including a plurality of carriers including aprimary and at least one additional carrier, the network comprising: atransmitter configured to transmit, to a user equipment (UE), a firstsignaling indicating which carrier among the plurality of carriers isconfigured as the primary carrier, wherein a carrier having a lowestcarrier index among the plurality of carriers is configured as theprimary carrier; a processor configured to activate an additionalcarrier of the plurality of carriers; wherein the transmitter is furtherconfigured to transmit, to the UE, a second signaling instructingremoving the additional carrier; and wherein the processor is furtherconfigured to remove the additional carrier based upon the secondsignaling.
 18. The network of claim 17, wherein the processor is furtherconfigured to configure another carrier of the plurality of carriers toa new primary carrier during a random access procedure.